This invention relates generally to a communications system, and more particularly to a satellite-based communications systems where the satellite includes an on-board cache for Internet web information.
Access to an internet is imperative for most computer users today. Public and private internets provide an especially convenient means for exchanging information.
Internet users can quickly transmit data to others internet-connected sites, as well as research various subjects by downloading a variety of materials, such as text, graphics, and executable programs.
Although the term xe2x80x9cinternetxe2x80x9d is usually associated with the global and public Internet, there are both public and private internets. Private internets, often called xe2x80x9cintranetsxe2x80x9d or xe2x80x9centerprise internets,xe2x80x9d often have access limited to employees of a particular company. An internet is an open interconnection of networks, supporting the exchange of information among various attached computers. An internet includes a network of routing computers, which receive access requests and cooperatively route the requests to appropriate host computers capable of executing the request. Advantageously, routing computers and hosts may use almost any different type of architecture and operating system. Within an internet, communications are typically conducted under a standard protocol, such as Transmission Control Protocol/Internet Protocol (xe2x80x9cTCP/IPxe2x80x9d). Internets may employ a variety of electronic transport media, such as telephone lines, optical fiber, satellite systems, local area networks, etc. Users can access internets by a number of different means. In one example, a user""s computer connects to a host computer directly via telephone line, cable television line, ISDN line, or another line, the host computer itself being coupled to internet routers by a T3 connection or other suitably fast link. In another example, a user""s computer may be coupled to a network, such as a local area network, which connects to an internet by an appropriate means, such as a T3 connection.
Although the depth of information available through internets is nearly unlimited, there are definitely limits to internet access speed. Even the fastest internet access links can only carry so much data in a given period of time. Due to the limited communications bandwidth of internet access links, internet users may confront a number of different penalties. For example, users with local network connection to an internet may experience slow download times because of the local network""s internet workload from other users. In this case, since the network server operates as a conduit to the internet, it may be burdened by many different simultaneous user requests to download information from the internet. In a corporate intranet environment, users can suffer from slow network performance despite whether their particular download request is urgent or not. For example, one user with a particularly urgent request to download critical accounting information may be delayed because of many other users busy obtaining weather information, checking stock prices, idly xe2x80x9csurfing the net,xe2x80x9d and doing other less urgent tasks. Especially frustrating is the fact that burdensome internet access tasks can prevent the network server from efficiently completing other processing tasks, completely unrelated to internet access.
For instance, a large number of concurrent internet communication requests may slow the network server""s completion of spreadsheet programs, personal calendars, mathematical computations and modeling, and other programs running on the network on behalf of individual users. On the other hand, users that individually connect to the internet can avoid many of the problems experienced with internet access through local networks. Nonetheless, users with individual internet connect on still encounter different problems of their own. If the user""s internet link is a telephone line, for example, long downloads may result in higher charges from the telephone company, and longer periods during which a shared telephone line is unavailable for other purposes, such as voice calls and fax use. Consequently, known approaches to internet access are not completely adequate for some applications due to certain unsolved problems.
One potential scheme utilized to minimize the problem has involved the use of a server to selectively filter and cache internet access requests from the terminals attached to the server, and subsequently resubmit the cached requests appropriately. Web caches bring two main benefits to an Internet Service Provider (ISP): improved response times and more efficient use of bandwidth. Deploying a cache significantly reduces the xe2x80x9cworld wide waitxe2x80x9d problem-by storing Web objects closer to end users. If the requested objects are in the cache, they get the information almost instantaneously, while requests that have to go to the remote web server typically take several seconds to be fulfilled.
Second, caches reduce traffic and ultimately save ISPs money by decreasing their bandwidth costs by as much as 50 percent. When users get objects from caches, they do not use as much bandwidth as if the object came from the origin server. This is of high importance to ISPs as they grow their business and expand their customer base.
An illustration of this system is presented in FIG. 1. The internet 12 in this context may be the worldwide public Internet, or a private. xe2x80x9centerprisexe2x80x9d internet such as a corporate xe2x80x9cintranet.xe2x80x9d Since the browsers or terminals 14 are connected to the internet via the server 16, the server 16 is a focal point for all internet requests. Initially, the server 16 receives a request from one of the attached terminals 14 to download desired information from the internet 12. The received request contains a download code, such as a universal resource locator (xe2x80x9cURLxe2x80x9d), identifying the desired information page 18. The server 16 determines whether the requested page 18 has previously been cached within the server 16. If it has, the server 16 does not forward the request to the internet 12, but instead replies directly to the terminal 14 with the copy 20 of the requested page 18. If the cache 22 within the server 16 does not contain a copy 20 of the requested page 18, the server 16 forwards the request to the internet 12, which then routes the request through remote we servers 24 to obtain the page 18. The page 18 is then obtained from the web servers 24, and transmitted through the internet 12 to the server 16 and thence to the requesting browser 14.
The extent of the benefits of caching are directly related to the xe2x80x9chit ratexe2x80x9d that the cache experiences. The xe2x80x9chit ratexe2x80x9d (requested content in cache divided by total requested content) is the primary driver both for improvements in average response time and for bandwidth savings. Hits are served instantaneously and do not consume bandwidth back to the origin server. Misses, on the other hand, take several seconds to be served and consume bandwidth. A well designed cache achieves hit rates of 30 to 60 percent of Web traffic, depending on size and diversity of the end user community, the size of the cache and the caching algorithms used. For certain types of requests, traffic hit rates can reach 90 percent.
With the advent of satellite-based communications systems, such as that being contemplated under names Astrolink(trademark), Teledesic(trademark), Spaceway(trademark), and the like where internet traffic is transmitted wirelessly through space to and from the satellites to the distant ground stations and internet servers, the space transmission time delays alone associated with fetching a web page can amount to as much as 480 milliseconds. This makes the system appear to be slow and sluggish independent of available transmission speeds. Furthermore, since each request requires the use of four links, the bandwidth usage associated with each request is high.
What therefore would be desirable would be to provide a satellite-based communications systems where the delays and bandwidth usage are minimized.
The aforementioned need experienced in the prior art is met by the present invention, which provides a method for communicating internet data in a satellite-based communications system of the type including a satellite having a memory cache containing selected web pages, a standard user terminal 32 capable of receiving only one type of data transmission, an enhanced terminal 34 capable of receiving at least two types of data transmissions, and a ground station interconnected with the internet. The method functions by transmitting a request for a selected web page from either the standard user terminal 32 or the enhanced terminal 34 to the satellite. The satellite determines if the transmission came from a standard user or an enhanced terminal 34. If the request was transmitted from a standard user terminal 32, then the satellite relays the request for the webpage directly to the ground station. The ground station then retrieves the requested web page from the internet, and then transmits the requested web page to the satellite, where the satellite in turn takes the transmission and retransmits it to the user terminal 32. If the original request was transmitted from an enhanced terminal 34, then the satellite determines whether or not it already has a copy of the requested web page in its memory cache. If the satellite has a copy of the requested web page in its memory cache, the satellite processor retrieves the requested web page from its memory cache and transmits the web page to the enhanced terminal 34. If the satellite does not have a copy of the requested web page, it in turn requests the web page from the ground station, which then obtains the page from the internet, transmits it to the satellite, and the satellite in turn retransmits the requested web page to the enhanced terminal 34.